DK174411B1 - Method for control of wind turbine under periods of electrical network connection cutoff - Google Patents

Abstract

Procedure for control of a pitch-controlled wind turbine under periods of electrical network connection cutoff and subsequent re-establishment of connection with the network, where the wind turbine includes a network-connected generator, which is driven by a wind turbine rotor, includes the following steps:a) carrying out of condition measurements, with the aim of detecting conditions which demand cutoff and subsequent conditions which permit re-establishment of connection between the generator and the networkb) when the generator is cut off from the network, on the basis of the condition measurements, control of the wind turbine is established which ensures a rotation speed for the rotor and the generator which is within the normal range of speed for thesec) when re-establishment of network connection is permitted, on the basis of the condition measurements, connection to the generator is re-established, andd) normal operation is resumed.With this procedure it is made possible to bring about a rapid re-establishment of connection to the power network, as soon as such a re-establishment of the connection is allowed, and the wind turbine is controlled during the cutoff in such a way that it is ready for re-establishment of connection with the network and without mechanical overload of the wind turbine, whereby the wind turbine will be in condition to contribute to the stabilization of the network after a fault in this.

Description

5 DK 174411 B1

TECHNICAL FIELD The present invention relates to a method for controlling a wind turbine during periods of interruptions from the grid, of a kind as defined in the preamble of claim 1.

Prior Art In wind turbines of this kind, it is known, upon disconnection of the generator, to perform an emergency braking to a full stop of the wind turbine, by quickly setting the pitch angle to 90 ° 10 or "edge position" where the pitch angle is defined as the angle between the planes of the blades A method of this kind is known from US 5,907,192 where the rotational energy stored in the rotor is used to generate power to the pitch control system and the control system during emergency braking after disconnecting the generator from the supply network. uncontrolled rapid braking, which may result in mechanical overload of the wind turbine construction, and this document does not mention any measures to control the wind turbine in a "ready to reconnect" rotary state.

Disclosure of the Invention 20

It is the object of the present invention to provide a method for controlling a wind turbine during periods of disconnection from the supply grid, of the kind set forth above, by which it is possible to achieve a rapid reconnection when a throughput is allowed, and this method provides an opportunity to control the rotation of the wind turbine during such periods of disconnection from the supply network, ready for reconnection, preferably without mechanical overload, and this is achieved by a method of controlling a wind turbine during periods of disconnection from the supply network of the kind mentioned in accordance with the present invention also includes the features set forth in the characterizing part of claim 1. With this arrangement, the wind turbine will be controlled rapidly at disconnection from the supply grid at a rotational speed ready for reconnection after removal of a possible failure of the supply grid, whereby the wind turbine will be able to contribute to the supply network stabilization after such a failure in the supply network, where such errors typically have a duration of a few seconds.

35 2 DK 174411 B1

Preferred embodiments, the advantages of which will be apparent to those skilled in the art upon reading the following detailed description, are disclosed in the subordinate claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed part of the present description, the invention is explained in more detail with reference to the exemplary embodiments of a method for controlling a wind turbine during periods of disconnection from the supply grid, in accordance with the invention, as shown in the drawings, wherein FIG. 1 schematically shows typical Cp curves of the rotor blades of a wind turbine; FIG. 2 shows a curve indicating pitch angle as a function of wing tip velocity ratio for obtaining a rotor power equal to zero; and FIG. 3 schematically shows a block diagram of a preferred embodiment for implementing the method in accordance with the present invention.

Description of the Preferred Embodiment 20

Fig. 1 shows the typical Cp curves for a wind turbine, ie. the power utilization of the wind turbine rotor as a function of pitch angle 8 and wing tip velocity ratio λ, where λ is defined as λ = R x ojR / wind, where R is the rotor radius, oaR is the rotor speed and Vvmd is the wind speed. In order to determine a pitch angle 80 which will provide a rotor power equal to zero, the following equation must be solved: Ορ (80, λ) = 0 The solution to this equation is shown in Figure 2, which indicates the zero power pitch angle 80 as 30 a function of λ.

FIG. 3 shows a preferred implementation of the method in accordance with the present invention, comprising a wind estimator 1 for providing a wind speed vvmd for calculating λ. The wind estimator could be replaced by a simple wind measurement or a more complex wind speed prediction unit. The measured rotational speed of the rotor ojmeas and vvin <j is used in λ calculator 2 and λ 3 t DK 174411 B1 is used as a parameter for a table lookup calculation 3 of 80 During normal operation, an optimal pitch angle 8opt of the control system 4 is used and is used as pitch angle reference Srer for the pitch control and the mechanical system which controls the pitch angle & for the rotor blades, the pitch angle & measuring Smeas. During normal operation, various conditions are detected which could require disconnection between the generator powered by the wind turbine and the supply network. Such conditions could be a short circuit in the supply grid, but other possible conditions could be conceived, such as other faults in the supply grid or in the generator and possibly high mechanical loads somewhere in the wind turbine, etc.

10 When such states requiring interruption are detected 6, pitch reference 9ref is switched from 8opt to 80 by the state detector 6, whereby the pitch angle reference is quickly changed to 80 when the generator is disconnected from the supply network. The result of this is that the wind turbine rapidly reduces its power uptake from the wind to about zero, thereby avoiding over-speed of the wind turbine when power is no longer supplied. In the embodiment shown in Figure 3, an additional control loop is included for the wind turbine. controlling the wind turbine at a constant rotational speed ωΓβί, using a velocity controller 7, which receives the measured velocity oomeas and the reference velocity as input signals, respectively, and delivers a velocity-controlling pitch angle 8sp to the pitch control system. 8sp is not connected to Sfer before 8 deviates less than, for example, 0.5 ° from 80, as detected by the angle difference detector 8. This means that as soon as the measured pitch angle 8meas deviates less than 0.5 ° from S0l, the reference pitch angle 8re is shifted to the speed control pitch angle 8sp.

As soon as the fault condition is removed, the generator can be reconnected to the supply grid and normal operation can be resumed with the pitch angle controlled in accordance with the optimal pitch angle & opt emitted from the control system 4. Of course, the 8opt must be increased slowly from the actual pitch angle 8 immediately before resuming normal operation. , in the same way as during normal start-up of the wind turbine.

As an alternative or in addition to the pitch control described above, a braking system may be used to control the rotational speed of the wind turbine rotor upon disconnection from the supply grid. In this regard, the braking system should, of course, be dimensioned to be capable of delivering the required power, and this requirement can be reduced by combining the braking system control and pitch control in such a way that the pitch control completely takes over the control after a short period of time. braking control.

5

It will be apparent to those skilled in the art that several modifications of the preferred embodiment as described above may be conceived. Thus, the method could be implemented without the speed control loop 7 and using a fixed 90 during disconnection from the supply grid, whereby the rotational speed of the wind turbine ω would vary depending on the wind speed but close to the rotational speed immediately before the interruption, using the fixed value of 90, which is calculated at the time of the interruption. Further, the calculation of 90 could be based on a negative rotor effect, which would cause the rotor to decelerate before switching to speed control, which could be an advantage to avoid over-speed. Further, the measurement of the rotor speed iumeas could be replaced by a measurement of the generator speed. The choice of the reference speed cure (may depend on various parameters of the wind turbine, and for a pitch controlled wind turbine at a fixed speed with an induction generator, the speed reference should be set equal to the synchronous speed of the generator, in order to avoid high starting currents at the time of connection re-establishment Further, this speed reference wref could be determined by the wind speed, the measured speed or the speed reference, immediately before the disconnection from the supply network, etc. 25 A further advantageous control of the pitch comprises the calculation of 90 to provide a negative rotor power of, for example, 50% of the rated power. and switching to speed control as soon as the speed is lower than a maximum static speed of the wind turbine and the difference between the pitch angle 9meas and pitch reference 90 is less than 0.5 °.

Claims (14)

5 DK 174411 B1! A method of controlling a pitch-controlled wind turbine during periods of disconnection from the grid and subsequent re-establishment of the connection, said wind turbine comprising a grid-connected generator powered by the wind turbine rotor, characterized by comprising the following steps a) performing state measurements, for the purpose of: detecting conditions requiring disconnection and subsequent states which allow the connection to the generator to be restored, b) when the generator is disconnected from the grid, based on the state measurements, establishing a control of the wind turbine which ensures a rotational speed of the rotor and the generator within it. normal speed range, c) when the reconnection of the generator is permitted, based on the state measurements, the reconnection of the generator to the generator, and d) resumption of normal operation. The method according to claim 1, characterized in that step b) comprises establishing a control of the wind turbine which ensures a rotational speed of the rotor and generator 20 within the normal speed range, using a braking system which may already be available for emergency braking and stopping. of the wind turbine. Method according to claim 1, characterized in that step b) comprises establishing a control of the wind turbine which ensures a rotational speed of the rotor and generator 25 within the normal speed range, further comprising: b1) determining a pitch angle 90 which will provide a predetermined rotor power or predetermined rotor torque less than or equal to zero, and b2) when the generator is disconnected from the grid, based on the state measurements, the pitch reference is set to the determined pitch angle 90- Method according to claim 1, characterized by comprising a combination of the features according to claims 2 and 3. 35 6 DK 174411 B1 Method according to claim 3, characterized in that the following step b3) follows step b2): b3) when the measured pitch angle 9 is greater than or equal to θ0 - Δ90) where Δ90 is a small deviation of, for example, less than 1 °, the wind turbine is put into a speed control mode where the speed of the rotor is controlled to a predetermined reference speed U) located within the normal speed range of the wind turbine rotor. Method according to claim 5, characterized in that Δ90 is less than 0.5 °. A method according to any one of the preceding claims 5-6, characterized in that the predetermined rotor reference speed ω0 is determined depending on the measured, estimated or predicted wind speed and / or set or measured rotor speed before interruption. Method according to any of the preceding claims 5-7, characterized in that step b3) further comprises setting up an additional condition that the rotational speed must be less than or equal to the predetermined speed ω0 before switching to speed control. Method according to any of the preceding claims 3-8, characterized in that step b1) comprises determining a pitch angle 90 which provides a rotor power between zero and -100%, preferably about -50% of the nominal rotor power. 25 Method according to any one of the preceding claims 3-9, characterized in that step b1) comprises determining pitch angle 90 based on parameters selected from the following list: i) measured rotor speed (ω) (or corresponding generator speed), ii) rotor speed reference ( coref) (or equivalent generator speed reference), ni) measured wind speed, iv) predicted wind speed, v) estimated water speed, 35 and the determination of pitch angle 90 are based on calculations and / or table lookups. j DK 174411 B1 ί '7 Method according to any one of the preceding claims 3-10, characterized in that the pitch angle S0 is a fixed angle until possible speed control mode is set, i.e. based on fixed starting parameters. 5 Method according to any one of claims 3-7, characterized in that pitch angle 30 is a dynamic angle based on the parameters i) to v) of claim 10 as well as calculation and / or table lookup. DK 174411 B1 Cp a 0. $ - 1-11 I --- '1 "- i' i" I "I i 1 i 0-3 * - - I -" t ί 'I * "" "I * - - r 'S ^' · i · - r 0.25 - - · * fj -i * i »- -» - - i * - * y ”i - \ ^ - f · - · - · *« ». // . /. \, · \. \. \. 0.CS - "" \ "'J' · - '' '-1 · \ * - ...... o - ^ \\\ - * - t —-- Λ-1 -; - i-1 - \ - 1 _ \ - 1 - λ O 2 4 SB 10 12 14 IB IB 20 Fig.1. 9o t 45 · Γ · ~ 1 “" Γ —T · "t I. i I 35. .............. 25 · - - * \ * “1 *" "1" ', *' "1 *" 1 «*? 5.. "," · 1 * 1 - "" 1 "i * * '·'" 1 pi - «* 1 1 1 --- —1 - ^ -! .., I * λ, O 2 4 β 5 10 12 14 '16 <8 20' w Fig. 2 DK 174411 B1 (Λ ro Q) —- E CO ---, 1 77 = WI £ υ §E 2 t H LU O- C /} S CD -2 feh ------- / 'Λ * -, FS · -1 OO Vh \ o ----- <1 V CO _ ~ Tf o' Έ x, _ ^ CO | = O r— 'Or t § Island Island 1-Q.-Q- a 7 «y rV ^ - z o f— o: r — l— S? £ O csj tX fol tZ LU m CO ^ · __J ll o ii T7 r ~ £ =: CO <u LU E o _ w 1